Synthesis and characterization of carbon quantum dots by microwave-assisted pyrolysis method from citrus juices and application in fluorescent bioimaging

Abstract

Carbon quantum dots (CQDs) are carbon-based nanoparticles which are less than 10 nm in size and are characterized by having modulable properties of luminescence and conductivity while presenting low toxicity, high water solubility, and biocompatibility, among others. These characteristics make them a good option for possible applications in the industrial, chemical, and biomedical fields. In this study, carbon quantum dots were synthesized using juices of seven different fruits as precursors. The syntheses are carried out by microwave-assisted hydrothermal reaction at 200 °C, and reaction mixtures are purified by column chromatography, followed by characterization via absorbance, fluorescence, infrared spectroscopy and transmission electron microscopy. Comparison of relative concentration of CQDs after 2, 4, and 6 h of reaction show that the best quantum yield obtained (6.3 %) corresponds to the mandarin lime after 6 h pyrolysis (with excitation at 410 nm and maximum emission at 505 nm) with a 4.1 ± 0.8 nm particle size determined via transmission electron microscopy. The synthesized CQDs are shown to be usable in fluorescence bioimaging of Escherichia coli when excited at 450–490 nm, while few or no significant emission is observed at other excitation wavelengths (365 nm and 546 nm), which establishes complementarity and non-interference with other dyes that are used in bioimaging.